Combustion system deflector plate

ABSTRACT

A gas turbine engine combustion device having an annular intake for the flow of primary air into the combustion chamber. The intake is divided by deflecting means into two annular ducts. One main duct being provided for the main flow of primary air through the combustion chamber, the other duct providing a flow of air which is attached to the innermost wall of the deflecting means by the Coanda effect.

United States Patent 1191 Chesters Feb. 26, 1974 1' COMBUSTION SYSTEM DEFLECTOR 2,807,933 10/1957 Martin 60/39.72 R PLATE 2,965,303 12/1960 Jackson 60/3974 R 2,602,292 7/1952 Buckland et al. 60/3972 R [75] Inventor: Allan Knight Chesters, Delft,

Netherlands FOREIGN PATENTS OR APPLICATIONS 593,892 3 1960 C d 60 39.65 Assigneei Thesecl'etaly 0f state of Defence 607,893 11/1960 02:62.... 60/3965 London, England 201,618 7/1955 Australia 60/39.74 R 694,448 7/1953 Great Britain... 60/3965 [22] Sept 1971 723,830 2/1955 Great Britain 60/39.72 R [21] Appl. No.: 184,012

Primary Examiner-Carlton R. Croyle As rant Examiner-Robert E. Garrett [30] Forelgn Apphcatlon Pnomy Data Atft r rney, Agent, or Firm-Cushnian, Darby &

Sept. 26, I970 Great Britain 45,977/70 Cushman [52] US. Cl. 60/39.66, 60/39.74 R [51] Int. Cl. F02c 7/22 [57] ABSTRAFT [58] Field of Search. 60/3969, 39.72, 39.74, 39.65, A gas ,turbme engme Combustl?" Pavmg 60/39 66 nular intake for the flow of pnmary a1r mto the combustion chamber. The intake is divided by deflecting [56] References Cited mean:i isiitfo H310 annulzg ducts. One maintguct zetifig pr0v1 e or e mam ow 0 primary a1r roug e UNITED STATES PATENTS Y combustion chamber, the other duct providing a flow g i 2 of air which is attached to the innermost wall of the UI'gCSS B a 2,958,194 11/1960 Bayley deflectmg means by the Coanda effect 3,283,502 11/1966 Lefebvre 60/39.74 R 5 Claims, 2 Drawing Figures COMBUSTION SYSTEM DEFLECTOR PLATE This invention relates to combustion apparatus and is more particularly related to combustion apparatus for use in gas turbine engines.

In one form of gas turbine engine combustion apparatus, primary air enters the combustion chamber through a row of radially arranged swirler vanes which are located in an annular intake. This device imparts a swirl component to the primary air to promote mixing between the air and the fuel'but the discharge coefiicient of the device is relatively low and the film of air formed is relatively thick. A device having a higher discharge coefficient should give improved mixing because of the higher shear gradients and improved ignition performance because of the smaller film thickness which results from this higher coefficient.

The present invention seeks to provide a device for the intake of primary air which does not require swirler vanes and which has a higher discharge coefficient than a device having swirler vanes.

Accordingly the present invention provides a combustion chamber having an annular intake for the flow of primary air into the combustion chamber the annular intake being divided by deflecting means into at least two annular ducts, one said duct being for the main flow of primary air into the combustion chamber whilst the other duct is for a flow of air which is attached to the innermost wall of the deflecting means by the Coanda effect when the combustion chamber is in operation.

The use of such a device should mean that the combustion apparatus wall temperatures are reduced because of the systematic way in which the flame gas proceeds towards the walls and the lack of unstable interchange of non-swirling wall cooling air with the air which has passed through the swirler vanes.

The deflecting means may comprise an annular deflecting plate which includes a cylindrical portion opening out into a bell-mouth portion in the downstream direction.

The deflecting means may be supported on a plurality of vanes which extend between the combustion chamber wall and the deflecting means and produce non-swirling flow.

Other vanes may be arranged in the other duct to impart swirl component to the air flowing through the other duct but these last-mentioned vanes are preferably aerofoil vanes to produce a non-swirling flow.

The invention can be equally well applied to the tubular, tuboannular and annular types of combustion chamber.

The present invention will now be more particularly described with reference to the accompanying drawing in which FIG. 1 shows a diagrammatic part-elevation of one form of combustion chamber according to the present invention and FIG. 2 shows a diagrammatic part-elevation of a further form of combustion chamber according to the present invention.

In the drawing, a combustion chamber of a gas turbine engine has a flame tube head flare having an upstream cylindrical portion 12, and a circular deflecting plate 14 which is supported on the head flare 10 by a row of equi-spaced vanes 16 which are arranged to produce a non-swirling flow. A ring 18 is located on a fuel injector 20 and is attached to the deflector plate by a row of equi-spaced aerofoil vanes 21 which are arranged to produce a non-swirling flow but may be designed to impart a swirl component, if desired, and the deflector plate 14 has a cylindrical portion 14a and a downstream bell mouth portion 14b.

An annular intake 22 for the flow of primary air into the combustion chamber is defined between the cylindrical portion 12 and the ring 18 and the intake 22 is divided into two annular ducts 24 and 26 by the upstream cylindrical portion 14a of the deflector plate 14.

In order to ensure attachment of the main primary flow through the duct 24 to the walls of the flare 10, the outlet lip 14c of the deflector plate should extend beyond the outer wall of the duct 24, i.e., the diameter A B, and the angle 0 should be greater than or equal to the angle (1). It is also desirable to make the area of the duct 24 contract continuously in the downstream direction to aid attachment of the flow around the corner 28, thereby keeping the coefficient of discharge at a high value.

A film of air which flows through the duct 26 is made to attach to the curved innermost surface thereof the deflector plate by the Coanda effect to prevent carboning and heating of by the primary recirculation. At the start of the deflector plate curvature, the boundary layer flow is accelerated by the underpressure associated with the curvature and the flow being stable, remains attached. When the end of the curvature is reached, however, the boundary layer has to combat an adverse pressure gradient as the wall pressure is restored from an underpressure to the ambient pressure. The rise in wall pressure in relation to the dynamic head is dependent principally on t/R, where t is the rate of transfer of energy. and if t/R is less than a certain critical value, the rate of transfer of energy from the main flow to the boundary layer is sufficient to combat the adverse pressure gradient and the flow remains attached. When Rl-R2 and= the critical value of t/R is approximately 1/5.

The Coanda attached flow is required to protect the deflector plate from contact with the hot sooty recirculation and in order to prevent this recirculation from penetrating to the deflector plate wall, t/R should be greater than some critical value which is estimated as approximately l/l3. Therefore for satisfactory per- The edge E should be sharp witha; 45 to ensure detachment and the distance a which is the distance from the edge E to the start of the curvature of the deflector plate should not exceed 3!. The vanes 21 should be of aerofoil section, since the wakes left by even quite small bluff bodies have disastrous effect on the Coanda attachment.

The end face of the deflector plate is intended to accelerate the initial turbulent mixing between the main primary flow and the adjacent recirculation plus vaporised fuel, in a similar way to the large wakes found behind swirler vanes.

The edges E and E should be sharp not rounded to ensure detachment of the main primary flow and the Coanda attached flow from the plate.

With the arrangement described above it has been found that there is a substantial reduction of smoke at high engine power, improved ignition particularly at high altitude, improved cooling of the flame tube head flare and the normal film cooling which is used to cool downstream portions (not shown) of the combustion chamber is not broken down as is the case with flow pattern generated by swirler vanes.

The invention can be equally well applied to the tubular, the tuboannular and the annular type of combustion chamber and FIG. 2 shows the invention applied to the annular type of combustion chamber. In FIG. 2 an annular combustion chamber 30 has an annular deflection plate 32 which is supported on a number of equi-spaced vanes 34. The deflecting plate 32 comprises two circular members 36 and 38 which in combination provide a deflecting plate having an annular straight sided portion 32a and an annular bell mouth portion 32b.

The invention has been described with particular reference to gas turbine engines but it may be applied with advantage to other liquid fuel burners.

We claim:

1. Combustion apparatus comprising: a combustion chamber having a combustion wall, said wall having at least an annular upstream end portion and a head portion flaring outwardly from the downstream end thereof; fuel injection means carried within the annular upstream end portion of the combustion chamber wall and defining therewith an annular intake for the flow of primary air into the combustion chamber, said fuel injection means including a fuel injector surrounded by a ring member, said ring member being supported from the annular portion of said deflecting plate by a plurality of first vanes; a deflecting plate including an annular portion and a curved bell mouth portion, said annular portion being positioned between said fuel injection means and said annular upstream end portion of said combustion chamber wall to separate said air intake into at least two annular duets with a first duct being arranged radially outwardly of a second duct, said first duct being for a main portion of the flow of primary air into the combustion chamber, whereas said second duct is arranged for flow of a film of primary air, said curved bell mouth portion curving in the same direction as said combustion wall head portion flares; means to assist a Coanda effect to cause the film of air in said second duct to more closely follow the curved bell mouth portion of said deflecting plate, said means causing said film of air to detach from said fuel injection means downstream end, said means causing said film of air to detach from said fuel injection means including a sharp edge on the downstream end of said ring member positioned upstream of the curved bell mouth portion of said deflecting plate, said sharp edge of said ring having an angle of at least 45 with respect to an axis of said ring.

2. Combustion apparatus as claimed in claim 1 including a plurality of second vanes extending between the combustion chamber wall and said deflecting plate, said second vanes being non-swirling vanes.

3. Combustion apparatus as claimed in claim 2 in which said first vanes cause said film of air to swirl.

4. Combustion apparatus as claimed in claim 2 in which said curved bell mouth portion of said deflecting plate terminates in a sharp edge at a point radially outwardly of the axis of the fuel injection means further than said annular upstream end portion of said combustion wall.

5. Combustion apparatus as claimed in claim 4 in which said annular upstream end portion of said combustion wall and said annular portion of said deflecting plate are both cylindrical. 

1. Combustion apparatus comprising: a combustion chamber having a combustion wall, said wall having at least an annular upstream end portion and a head portion flaring outwardly from the downstream end thereof; fuel injection means carried within the annular upstream end portion of the combustion chamber wall and defining therewith an annular intake for the flow of primary air into the combustion chamber, said fuel injection means including a fuel injector surrounded by a ring member, said ring member being supported from the annular portion of said deflecting plate by a plurality of first vanes; a deflecting plate including an annular portion and a curved bell mouth portion, said annular portion being positioned between said fuel injection means and said annular upstream end portion of said combustion chamber wall to separate said air intake into at least two annular ducts with a first duct being arranged radially outwardly of a second duct, said first duct being for a main portion of the flow of primary air into the combustion chamber, whereas said second duct is arranged for flow of a film of primary air, said curved bell mouth portion curving in the same direction as said combustion wall head portion flares; means to assist a Coanda effect to cause the film of air in said second duct to more closely follow the curved bell mouth portion of said deflecting plate, said means causing said film of air to detach from said fuel injection means downstream end, said means causing said film of air to detach from said fuel injection means including a sharp edge on the downstream end of said ring member positioned upstream of the curved bell mouth portion of said deflecting plate, said sharp edge of said ring having an angle of at least 45* with respect to an axis of said ring.
 2. Combustion apparatus as claimed in claim 1 including a plurality of second vanes extending between the combustion chamber wall and said deflecting plate, said second vanes being non-swirling vanes.
 3. Combustion apparatus as claimed in claim 2 in which said first vanes cause said film of air to swirl.
 4. Combustion apparatus as claimed in claim 2 in which said curved bell mouth portion of said deflecting plate terminates in a sharp edge at a point radially outwardly of the axis of the fuel injection means further than said annular upstream end portion of said combustion wall.
 5. Combustion apparatus as claimed in claim 4 in which said annular upstream end portion of said combustion wall and said annular portion of said deflecting plate are both cylindrical. 